The present invention relates to an aircraft with a ventral fairing and to a seal for such an aircraft.
It is known that certain aircraft, provided with a fuselage and with a fixed wing structure comprising two wings which are opposed with respect to said fuselage, comprise a ventral fairing, generally projecting, in the form of a cradle, which is fixed to the underside of said fuselage where the latter meets said wing structure so as to close off the landing gear compartment, while possibly at the same time increasing the downward volume, and which has two longitudinal upstands reaching up the sides of said fuselage, said upstands each being provided with an opening for the passage of the corresponding wing. Such a fairing completes the aerodynamic profile of the intersection region and its shape is designed to minimize the aerodynamic drag that it generates.
In certain known aircraft, the method of attachment of this ventral fairing to the fuselage entails forming a peripheral slot around each wing, between the wing and the periphery of the corresponding opening of said fairing. In order to plug said slot, a seal is then provided which is fixed to the periphery of each opening and which comprises an elastic lip able, via the internal face of its free end, to press against the corresponding wing.
Now, in flight, because of the pressure difference between the pressure face side (at a raised pressure) and the suction face side (at a depression) of a wing, air begins to circulate within the fairing, through said slot, between the pressure face side and the suction face side of each wing and this, particularly on the suction face side, causes the free end of the elastic lip of said seal to detach from the corresponding wing. This gives rise to several drawbacks.
First of all, the elastic lip of the seal starts to vibrate in a frequency range which is perfectly audible from inside the cabin, and this proves annoying to the passengers. These vibrations are transmitted to the fuselage and to the elements it comprises (floor, support, etc.) and introduces structural fatigue loadings into said elements. In addition, the vibrations associated with the aerodynamic forces applied to said lip lead to premature fatigue thereof, which results in rapid wear which may go so far as to tear said lip. Finally, these vibrations cause parasitic aerodynamic drag to appear.
The object of the present invention is to overcome these drawbacks.
To this end, according to the invention, an aircraft comprising:
a fuselage and a fixed wing structure comprising two wings which are opposed with respect to said fuselage;
a ventral fairing in the form of a cradle, fixed to the underside of said fuselage, where the latter meets said wing structure, and provided with two longitudinal upstands reaching up the sides of said fuselage, said longitudinal upstands each being provided with an opening for the passage, with clearance, of the corresponding wing so that a peripheral slot is formed around each wing, between the wing and the periphery of the corresponding opening; and
a seal fixed to the periphery of each opening to plug said slot and comprising an elastic lip able, via the internal face of its free end, to press against the corresponding wing,
is notable in that, facing at least part of the suction face side of each wing, said internal face of the free end of said lip comprises at least one abutment boss able to keep said lip locally away from said suction face side so as to form a controlled leakage of air passing through said slot.
Thus, by virtue of the present invention, a controlled air leak is generated which eliminates, or at the very least greatly reduces, the vibration of said lip.
Depending on the geometry of the fuselage, of the wing structure and of the ventral fairing of the aircraft, the coefficient of pressure on certain parts of the suction face sides of the wings may be highly negative, which represents a great deal of suction, which means that the vibrations of the free end of the elastic lip may, at these points, have a great amplitude. It is therefore advantageous to apply the seal according to the present invention at least facing said parts of the suction face side at which the value of the coefficient of pressure is highly negative.
Of course, the height of each boss and the number of said bosses, and also their distribution, are determined, by calculation or by experiment, so that the flow rate of the air leak resulting from the presence of the boss or bosses generates very little parasitic drag, while at the same time ensuring that the lip of seal vibrates very little.
It will be noted that, in an aircraft, sealing is a constant concern to aircraft manufacturers because poor sealing may be the source of aerodynamic drag or of degradation to materials, through oxidation for example. For these reasons, the person skilled in the art is always seeking to obtain the best possible sealing of any space where there is a risk of leaks, and to do so in particular using devices specific to the geometry of the space that is to be filled (silicone sealant, very stiff seals, seals whose precise shape is tailored to the space that is to be filled, etc.). Thus, the present invention deviates from the prior art and organizes an air leak of controlled flow rate in order to solve a lack of sealing.
The present invention also relates to a seal for an aircraft comprising:
a fuselage and a fixed wing structure comprising two wings which are opposed with respect to said fuselage;
a ventral fairing in the form of a cradle, fixed to the underside of said fuselage, where the latter meets said wing structure, and provided with two longitudinal upstands reaching up the sides of said fuselage, said longitudinal upstands each being provided with an opening for the passage, with clearance, of the corresponding wing so that a peripheral slot is formed around each wing, between the wing and the periphery of the corresponding opening,
said seal being fixed to the periphery of said openings to plug said slot and comprising an elastic lip able, via the internal face of its free end, to press against the corresponding wing and being notable in that facing at least part of the suction face side of each wing, said internal face of the free end of said lip comprises at least one abutment boss able to keep said lip locally away from said suction face side so as to form a controlled leakage of air passing through said slot.
In the known way, said seal may comprise on its internal face, between the free end of said lip and the end of the seal that is intended to be fixed to the fairing, an additional sealing member able to press against the corresponding wing. Of course, just as has been stated hereinabove in respect of said lip, said additional sealing member may, in flight, be made to detach from the corresponding wing under the action of the circulation of air between the pressure face side and the suction face side, through said peripheral slot. Here again, by virtue of the presence of the bosses on the internal face of the free end of the elastic lip, the air leaks passing through said slot can be controlled.
Advantageously, said additional sealing member may be in the form of a radially elastic longitudinal tube. Thus, when the seal is applied to the wing structure of the aircraft, the tube, in coming to bear against a wing, deforms and flattens, offering a broad bearing area.
Said seal may additionally comprise a longitudinal recess in the form of a strip, provided on its external face, at the side of the end of the seal that is intended to be fixed to the fairing, and able to act as a housing for the periphery of the corresponding opening in the fairing. Thus, said seal can provide aerodynamic continuity between the fairing and the wing.
Said seal is advantageously produced in the form of a monolithic section piece, for example made of elastomeric material, possibly fibre-reinforced.